Electrically powered bistable thermal relay switch



Dec. 7, 1965 J. 1.. LORENZ 3,222,481

ELEGTRICALLY POWERED BISTABLE THERMAL RELAY SWITCH Filed April 10, 1963 2 Sheets-Sheet 1 INVENTOR.

JEROME L. LORENZ ATTORNEY E J. L. LORENZ Dec. 7, 1965 2 Sheets-Sheet 2 Filed April 10, 1965 .V R. W Y 5 Q: om m M 2 m m 3 w L. 7 w r .1 E 0 A i W R E Em fa g Y ..H|U N.@ B 3. N. m mm w 1/! v 7 l United States Patent 3,222,481 ELECTRICALLY POWERED BISTABLE THERMAL RELAY SWITCH Jerome L. Lorenz, Columbus, Ohio, assigrlor to Rauco Incorporated, Columbus, Ohio, a corporation of Ohio Filed Apr. 10, 1963, Ser. No. 271,898 4 Claims. '(Cl. 200-122) This invention relates to improvements in thermal relays, and more particularly to an improved thermal relay of the type utilizing an electrically heated bimetal to actuate contacts between a plurality of control positions.

It is a primary object of this invention to provide an improved thermal relay of the kind in which heat generated by a relatively small control current causes a bimetal member to operate a toggle switch mechanism alternately between first and second positions to control relatively heavy currents such as are required by electric motors driving refrigerating systems and the like, the switch being particularly suitable for operation as a bistable element in control circuitry providing a wide differential through relay energization at different heat levels corresponding to changes in the condition being controlled.

It is another important object of this invention to provide an improved electrically energized thermal relay which is capable of quick action yet can perform as a bistable control element which will remain in a first control position upon half power energization and be actuated to a second control position upon full power energization, which will remain in the second control position upon reduction of energization to half power, and return to its first control position upon reduction of energizing power to or near zero power.

It is another object of this invention to accomplish the bistable relay operation of the preceding paragraph by providing a bimetal power element which exerts a spring force which is a maximum in one direction when in a normal or unheated condition and which is a maximum in the other direction when heated by a predetermined electrical power, the bimetal element being inoperative when heated by half power to overcome a toggle spring force to move the switch contact, but operative to do so as either zero or full electrical power is approached. Preferably, the bimetal power element has a spring rate which is substantially less than the toggle spring rate so as to yield a large hysteresis loop in the force versus deflection characteristics of the bimetal as it actuates the switch through a complete cycle, the large hysteris loop being indicative of substantial potential energy being stored in the bimetal element upon heating and cooling, which energy is utilized to accelerate the toggle switch actuation.

Another object of this invention is the provision of an electrically energized thermal relay in which the efiective masses connected with a pivoted switch arm are evenly distriubted on opposite sides of the pivot point so as to minimize effects of mechanical shock and vibration to which the relay may be subjected, for example when installed as a control component on electrically driven mechanism refrigeration apparatus.

As another object this invention aims to provide an improved electric relay of the thermal or heated bimetal type comprising first and second bimetal elements acting in opposition to one another and operatively connected to a toggle switch mechanism, the first bimetal element providing the force for actuating the toggle switch in response to heat generated by an energizing current, preferably in a separate resistance heater adjacent the first bimetal, and the second bimetal member being operative to compenaste for changes in ambient temperatures "ice so that the electrical power requirements for actuating the relay between its first and second control positions remains substantially constant irrespective of ambient temperature effects on the first bimetal element.

Yet another object of this invention is the provision of a particularly compact, reliable, and inexpensive thermal relay of the foregoing character wherein the first and second bimetal elements lie in spaced parallel planes, with each element having a fixed end and a free end, the free ends extending in the same direction and being pivotally engaged with a transverse toggle switch driver member so that the bimetal elements and driver member define a rectangular space in which is disposed a movable contact acnrm and a toggle lever pivoted on a common axis and interconnected by an overcenter acting toggle spring engaging one end of the toggle lever, the other end of the toggle lever being acted upon by the driver member so that upon predetermined energization of the resistance heater, the first bimetal element will act through the driver member to cause the toggle lever and toggle spring to snap the contact arm between first and second control positions.

In a preferred embodiment of the device the fixed end of the second compensating bimetal is secured to support means which may be adjusted to increase or decrease the force by which the compensating bimetal opposes the first or actuating bimetal, whereby the range of operation of the relay will be selectively adjusted to respond to different predetermined energizing currents, or to vary somewhat the amount of time delay for actuation at a given full power energization.

The invention may be further said to reside in certain constructions and arrangements of parts by which the foregoing objects and advantages as well as others are achieved as will be readily understood from the following detailed description of a presently preferred embodiment of the invention read in conjunction with the accompanying sheets of drawings forming a part of this specification, and in which FIG. 1 is a side elevation of a thermal relay embodying the invention;

FIG. 2 is an enlarged sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a perspective view of the relay of FIG. 1 with the cover and resistance heater shown in disassembled relation;

FIG. 4 is a sectional view taken substantially along line 4-4 of FIG. 2; and

FIG. 5 is a graphical illustration of the force and deflection characteristics of the relay.

In the form of the invention shown in the drawings and described hereinafter, there is provided a bistable thermal relay 10 comprising a generally rectangular housing 11 of suitable dielectric material and having vertical side walls 11a and 1112, end walls and 11d, a bottom wall lle, and a cover 12 opposite bottom wall He. The cover 12 is conveniently secured by rivet posts 12a, as shown. Extending through the bottom wall He, and secured therein are a pair of conductor members 14 and 15 which terminate at the exterior of the housing in terminals 14a and 15a for connection to circuitry to be controlled. The inner ends of conductor members 14 and 15 comprise spaced parallel portions 14b and 1512 on which are mounted spaced stationary contacts 16 and 17 respectively. A third conductor member 18 is secured to the outside surface of bottom Wall 11:: by a rivet 20 extending therethnough, the conductor member ending in a terminal portion 18a.

The inner end of rivet 20 (FIG. 4) is axially bored to receive one end of a vertical pivot pin 21 with a press fit, Pivotally mounted on pin 21 is one end of a movable contact arm 22 the other end of which supports a double contact 23 which is disposed for movement between the fixed or stationary contact 16 and 17 to complete control circuits between terminal 18a and either of terminals 14a and a through arm 22.

The contact arm 22 is moved about pivot pin 21 by overcenter acting toggle means to shift contact 23 in opposite direction between contacts 16 and 17 with snap action. This toggle means comprises a toggle lever or arm 25 formed from sheet metal and having laterally spaced ears or bearing portions 26 disposed on opposite sides of the movable contact arm 22 and having aligned openings through which the pivot pin 21 extends. The bearing portions 26 are intermediate the ends 25a and 25b of the toggle arm, and the end 25a is provided with a V-shaped extension 250 which projects downwardly through a central opening 22a in the contact arm 22. The apex of the extension 250 serves as a seat for the otherwise free end 3011 of a bowed spring tongue 30 struck from the central portion of contact arm 22 and extending from adjacent the contact 23 into the opening 22a thereof. The bowed tongue 30 serves as toggle spring and will hereinafter be referred to as toggle spring 30.

Extending upwardly from the bottom wall 11a of the housing 11 are a pair of laterally spaced embossments which serve as stops 32 and 33 which limit the movement of the toggle arm 25 between the full line and dotted line positions thereof illustrated in FIG. 2. When the toggle arm 25 is in the full line position, the apex of extension 25c of the toggle arm'is above the center line of the contact arm 22 and the toggle spring 30 acts to hold contact 23 against the stationary contact 17. Upon rotation of the toggle arm 25 in a clockwise direction about the pivot pin 21 toward its dotted line positions, and as the end 30a of the toggle spring 30 passes to the opposite side of the contact arm 22, the contact 23 will be shifted from contact 17 to contact 16 with a snap action by the force of the toggle spring.

The just described toggle mechanism is adapted to be actuated to shift contact 23 between contacts 16 and 17 in response to electrical energization of a resistance type heater 35 by a predetermined control current. The heater 35 comprises a core 36 of heat resistant material such as mica supported at opposite ends by terminal members 37 and 38 extending upwardly through the cover 12. A winding 39 formed of nichrome wire or the like is supported by the core 36 and is connected at opposite ends to the terminal members 37 and 38, the winding generating heat in accordance with a control current applied to those terminals.

The heater 35 is mounted in close proximity to a first, or active bimetal power element 4-0 which is fixed at one end to a support member 41. The free end of the active bimetal 40 has a reduced portion 40a which is loosely received in an opening 42a at one end of a transversely disposed toggle driver member 42, which is conveniently formed of an insulating material such as micarta. The toggle driver member 42 has a second opening 42b loosely receiving a reduced end portion 250 of toggle arm 25. The driver member 42 is held on the ends 40a and 25d by laterally spaced, upstanding bearing members 44 against which the toggle driver member 42 is freely reciprocable.

The active bimetal 40 has its side of greater coefiicient of expansion facing the heater 35 so that energization of the heater will causethe bimetal 40 to move its free end and the toggle driver 42 in a direction causing clockwise movement of the toggle arm 25 and actuation of the contacts 23 from the stationary contact 17 to the stationary contact 16. Cooling of the bimetal 40 upon deenergization of the heater 35 will cause the toggle driver member 42 to move in the opposite direction so as to effect counterclockwise rotation of the toggle arm 25 and actuation of the contact 23 to its full line position against contact 17.

In order to compensate for ambient temperature effects on the active bimetal 40, there is provided a second or ambient compensating bimetal element 50 having one end secured to one leg 51a of an adjustable U-shaped support member 51 and having a reduced portion 50a at its free end engaged in an opening 420 in the toggle driver member 4-2. The compensating bimetal 50 lies in a plane which is spaced and parallel to that of the bimetal and has its side of greater coeflicient of expansion disposed outwardly so that the force effects of ambient temperature changes on bimetal cancels the force effects of those ambient temperature changes on the bimetal 40, the bimetal 50 acting in opposition to the bimetal element 40 through the toggle driver member 42.

The adjustable U-shaped support member 51 for the ambient compensating bimetal 50 comprises a second leg 51b lying parallel to the housing rear wall 11b and having an inturned lug 51c riveted to the bottom wall lie of the housing as shown at 52. An adjusting screw 54 is threadedly received in an opening in leg 51b and has its end bearing against the leg 51a. The head 54a of the screw 54, which is conveniently provided with a screw driver slot, is accessible through an opening 55 in the housing wall 11b. The screw 54 may be advanced or retracted in leg 51b to change the angular position of leg 51a with respect to leg 51b, it being understood that leg 51a is resiliently self-biased toward leg 51!).

By changing the angular position of leg 51a with respect to leg 51b, the force of the compensating bimetal 50, on the active bimetal 40 may be varied to select the temperature or predetermined energizing power at which the bimetal 40 will develop sufficient force to actuate the toggle switch. Thus, the compensating bimetal 50 serves a double purpose as both a compensating element and a calibrating load spring.

The bimetal element 40 is resilient in the nature of a leaf spring and is selected to have a spring rate which is appreciably less than the spring rate of the toggle spring 30. This selecting of relative spring rates provides a desirable deployment of energies in the operation of the relay which will now be described.

It will be seen that when the parts of the relay are in the position shown in FIG. 2 spring tongue 30 not only urges contact arm 22 toward fixed contact 17, but it also urges levers 25 counterclockwise, having its line of force above a line through pivots 21 and 250 of lever 25, thereby yieldingly resisting upward movement of driver 42. As driver 42 tends to rise by action of bimetal 40 and overcomes the downward component of force exerted by tongue 30, lever 25 will commence to rotate clockwise, shifting pivoted end 3001 of spring 30 toward a line through pivot points 21 and 25c and the centerline of arm 22, which immediately reduces the components of force of spring 30 on the arms 22 and 25 so that this occurrence with the resiliency of bimetal 40 effects a snap movement of the switching mechanism to its reversed position, in which end 250 rests on stop 33. In this position, pivoted end 30a of spring tongue 30 is below the centerline of contact arm 22 and also below a line through the pivots 21 and 25b of levers 25 so that tongue 30 not only urges arm 22 toward fixed contact 16, but reacts on lever 25 to urge it clockwise about pivot 21 and resist downward movement of driver 42. As bimetal 40 cools to resiliently urge driver 42 downwardly, the opposing force of lever 25 on the driver is finally overcome and as soon as movement of pivoted end 30a of tongue 30 commences to move toward the centerline of contact arm 22, the force of tongue 30 collapses and the resiliency of bimetal 40 then combines with this action to cause a snap movement of the switch parts to the positions shown in FIG. 2.

In selecting the bimetal element 40 and tongue 30, the spring rate characteristics thereof and the heating capacity of heater 35 are chosen so that the reaction of toggle spring 30 resists flexing of the bimetal in both directions so that the initial switch shifting movement described cannot be effected except where the bimetal is heated to a degree only possible by full energization of the heater and the switch will retain its shifted position although the bimetal cools appreciably due to a reduction in heating capacity of the heater to approximately 50% of full heat. The construction shown, permits the relay to function effectively as a bistable control element.

Referring now to FIG. 5, in which the vertical axis represents force and the horizontal axis represents deflection, the force and deflection characteristics of toggle spring 30 on movable contact arm 22 are denoted by a full line curve 60, while the force and deflection characteristics of the bimetal member 40 are denoted by the dot and dash line curve 61. Starting at point A with the relay completely deenergized, the deflection of the bimetal 40, the toggle spring 30, and the toggle lever 25 will be limited by engagement of the toggle lever with the stop 32. Upon half power energization of the heater 35, the force exerted by the bimetal 40 against the toggle spring through the toggle lever 25 will increase as indicated by dot and dash line 61 from A to B but will be insufficient to effect movement of the toggle arm and spring, and hence at half power the switch will remain stable in its first operative position with contact 23 against contact 17.

Upon full power energization of the heater 35, the force of bimetal 40 will increase going from B to C and when the force of the bimetal equals the force of the toggle spring 30 at point C, the toggle lever 25 is rotated away from stop 32 toward stop 33 and the toggle spring force degenerates with acceleration toward zero as indicated by the full line 60, at which point the toggle spring drives the movable contact 23 into engagement with the fixed contact 16, and the toggle lever 25 ,comes .to rest against stop 33. These movements are accompanied by an expenditure of energy by the bimetal member 40 and decrease in force thereof as indicated by the slope of the dot and dash line 61 from C to D. Thereafter, continued full power energization of the heater results in an increase of force in the bimetal member 40 from D to an equilibrium condition at E without further deflection.

Reduction of energization of the heater 35 from full power to half power will effect a corresponding reduction in force of the bimetal 40 from point B to point F without any change in'deflection of the toggle, whereby it can be seen that the relay is also stable in its second operative position with contact 23 against contact 16 when energized at half power. Upon complete denergization of the heater 35 to zero power, the bimetal 40 will cool and exert an increasing force from F to G at which point the force of the toggle spring 30 on the toggle'lever 25 will be overcome and will rapidly a-ccelerate toward zero as the toggle lever is moved from stop 33 toward stop 32. After the toggle spring effective force passes through zero, as indicated by the full line curve 60, the toggle spring will drive the movable contact 23 rapidly from contact 16 to contact 17. These movements of the toggle lever 25, spring 30 and movable contact are accompanied by movement of the bimetal 40 and expenditure of energy thereof, thereby resulting in a reduction of force by the bimetal as indicated by the sloping dotted line from G to H. Thereafter, as the bimetal 40 cools to an equilibrium condition, the force exerted thereby will increase as represented from H to A without any further deflection.

It will be recongnized from inspection of the large hysteresis loop described by the line 60 representing the force and deflection characteristics of the bimetal 40 during a complete cycle of operation, and because of the differential in spring rates of the bimetal 40 and the toggle spring 30, a substantial amount of energy is stored in the bimetal as it develops the necessary force to actuate the toggle mechanism, and that this energy is utilized to advantage to aid in accelerating the operation of the toggle switch.

From the foregoing detailed description of a preferred embodiment of the invention, it will be appreciated the invention accomplished the aforementioned objects and provides an improved electrically energized thermal relay which is bistable at half power, is compensated for ambient temperature changes, is adjustable to select a required actuating temperature or predetermined energizing power, and yet is compact, reliable, and resistant to shock or vibration.

Although the described embodiment has two fixed contacts 16 and 17 between which the movable contact 23 operates, it will be recognized that other contact arrange ments could be used and that other changes could be made without departing from the spirit of the invention. For example, one of the fixed contacts could be eliminated for single pole, single throw service.

Accordingly, although the invention has been described in considerable detail with reference to a specific relay embodying the invention, the invention is not limited thereto, but rather the invention includes all those changes, adaptations, modifications, substitutions and uses as are reasonably embraced by the scope of the claims hereof.

Having described my invention, I claim:

1. A thermal relay of the bistable character described comprising:

(a) support means,

(b) toggle switch means mounted on said support means and comprising a toggle lever and a switch arm pivoted about .a common axis, stop means for limiting rotation of said toggle lever in opposite direction, and a toggle spring between one end of said lever and said arm for biasing the latter into first and second operative position upon rotation of said toggle lever between said stop means and through an overcenter position, said toggle spring being effective to resist movement of said toggle lever from said stop means with a predetermined force,

(c) a toggle driver member connected to the other end of said lever and reciprocable to effect said rotation thereof,

((1) an elongated bimetal element having one end fixed to said support means and the other end connected to said driver member,

(e) an electrical resistance heater mounted on said support means and adjacent said bimetal element in radiative heat transfer relation thereto,

(f) said bimetal being operative upon predtermined heating and cooling to effect said rotation of said toggle lever, yet having a spirng rate which is less than the spring rate of said toggle spring, and

(g) said bimetal element being inoperative to effect said rotation of said toggle member upon less than said predetermined heating or cooling thereof, whereby said relay is bistable at less than a predetermined electrical power of energization.

2. A thermal relay comprising:

(a) support means,

(b) toggle switch means mounted on said support means and comprising a toggle lever and a switch arm pivoted about a common axis, and a toggle spring between one end of said lever and said arm for biasing the latter into first and second operative positions upon rotation of said lever in opposite directions through an overcenter position,

(c) a toggle driver member connected to the other end of said lever and reciprocable to effect said rotation thereof,

(d) a first elongated bimetal element having one end fixed to said support means and the other end connected to said driver member,

(e) a second elongated bimetal element having one end secured by adjustable mounting means to said support means and the other end connected to said driver member, i

(i) said bimetal elements having their sides of greater expansion facing in opposite directions so as to cancel ambient temperature change effects thereon,

(g) said bimetal elements extending in spaced parallel relation to one another with said driver member transverse thereto to define a rectangular space, said toggle switch means being disposed in said space,

(h) an electrical resistance heater mounted adjacent one of said bimental elements in radiative heat transfer relation thereto,

(i) said one bimetal being operative upon predetermined heating and cooling to effect said rotation of said toggle lever, yet said first and second bimetal elements having a combined spring rate less than the spring rate of said toggle spring, and

(j) said one bimetal being inoperative to effect said rotation of said toggle member upon less than said predetermined heating or cooling thereof, whereby said relay is bistable at less than a predetermined electrical power of heater energization.

3. A thermal relay comprising:

(a) a support structure,

(b) a toggle lever having bearing means intermediate its ends,

() means supporting said lever on said support structure comprising a pivot pin extending transversely of said lever and through said bearing means,

(d) a contact arm journaled at one end on said pin and co-extending with and beyond one end of said toggle lever,

(e) means on said support structure including an electric contact forming spaced stops between which the other end of said contact arm moves,

(f) a toggle spring connecting said one end of said toggle lever and the portion of said contact arm extending beyond said lever, said toggle lever being movable about its pivot to shift the centerline of force of said spring from one side to the other side of the centerline of said contact arm,

(g) an elongated actuating member pivotally attached to the other end of said toggle lever and projecting transversely thereof, and

(h) a pair of bimetal strips each supported at one end to said frame and operatively attached at their other ends to opposite ends of said actuating member, respectively.

4. A thermal relay comprising:

(a) a box structure including a bottom wall and an end Wall,

(b) a pivot pin supported at one end in said bottom Wall and projecting normal thereto,

(c) a toggle lever having bearing means intermediate t3 the ends thereof pivoted on said pin to swing in a plane parallel to said bottom wall,

(d) spaced abutments formed on said bottom wall and projecting in the path of one end of said toggle lever to limit movement thereof,

(e) a flat contact arm pivoted at one end to said pin and extending between said spaced abutments and beyond said toggle lever, arm having an elongated opening therein through which said end of said toggle lever may pass,

(1) a contact carried by the other end of said contact arm,

(g) a pair of spaced stops supported on said bottom wall and between which said contact arm moves and which stops limit movement of said arm about its pivot,

(h) a bowed compression spring pivotally connected at one end to said one end of said toggle lever and connected at the other end to said contact arm at one end of said elongated opening,

(i) said toggle lever having a segment extending beyond the pivoted end of said contact arm and terminating adjacent said end wall,

(i) an elongated toggle drive member extending transversely of the end of said segment and having an opening receiving an end portion of the other end of said toggle lever,

(k) a pair of bimetal strips extending generally parallel to said toggle lever and contact arm and located on the outer sides of said abutments respectively,

(1) means supporting one end of said bimetal members, the opposite ends the respective bimetal strips being received in openings in opposite end portions of said toggle drive member, and

(m) abutment means on said end wall and engaging said drive member to maintain said drive member in engagement with said bimetal strips and toggle lever.

References Qited by the Examiner UNITED STATES PATENTS OTHER REFERENCES Widmaier, German printed application 1,077,333,

March 1960.

BERNARD G. GILHEANY, Primary Examiner. 

1. A THERMAL RELAY OF THE BISTABLE CHARACTER DESCRIBED COMPRISING: (A) SUPPORT MEANS, (B) TOGGLE SWITCH MEANS MOUNTED ON SAID SUPPORT MEANS AND COMPRISING A TOGGLE LEVER AND A SWITCH ARM PIVOTED ABOUT A COMMON AXIS, STOP MEANS FOR LIMITING ROTATION OF SAID TOGGLE LEVER IN OPPOSITE DIRECTION, AND A TOGGLE SPRING BETWEEN ONE END OF SAID LEVER AND SAID ARM FOR BIASING THE LATTER INTO FIRST AND SECOND OPERTIVE POSITION UPON ROTATION OF SAID TOGGLE LEVER BETWEEN SAID STOP MEANS AND THROUGH AN OVERCENTER POSITION, SAID TOGGLE SPRING BEING EFFECTIVE TO RESIST MOVEMENT OF SAID TOGGLE LEVER FROM SAID STOP MEANS WITH A PREDETERMINED FORCE, (C) A TOGGLE DRIVE MEMBER CONNECTED TO THE OTHER END OF SAID LEVER AND RECIPROCABLE TO EFFECT SAID ROTATION THEREOF, (D) AN ELONGATED BIMETAL ELEMENT HAVING ONE END FIXED TO SAID SUPPORT MEANS AND THE OTHER END CONNECTED TO SAID DRIVER MEMBER, (E) AN ELECTRICAL RESISTANCE HEATER MOUNTED ON SAID SUPPORT MEANS AND ADJACENT SAID BIMETAL ELEMENT IN RADIATIVE HEAT TRANSFER RELATION THERETO, (F) SAID BIMETAL BEING OPERATIVE UPON PREDETERMINED HEATING AND COOLING TO EFFECT SAID ROTATION OF SAID TOGGLE LEVER, YET HAVING A SPRING RATE WHICH IS LESS THAN THE SPRING RATE OF SAID TOGGLE SPRING, AND (G) SAID BIMETAL ELEMENT BEING INOPERATIVE TO EFFECT SAID ROTATION OF SAID TOGGLE MEMBER UPON LESS THAN SAID PREDETERMINED HEATING OR COOLING THEREOF, WHEREBY SAID RELAY IS BISTABLE AT LEASS THAN A PREDETERMINED ELECTRICAL POWER OF ENERGIZATION. 